IRS Form 6166 (Certification of U.S. Tax Residency)

IRS Form 6166 — formally titled the Certification of U.S. Tax Residency — is an official letter issued by the U.S. Internal Revenue Service confirming that a person or business is a U.S. tax resident for a given tax year. It is the document most foreign tax authorities require before granting reduced withholding rates, treaty benefits, or VAT refunds under a U.S. tax treaty. Because Form 6166 is a federal document, the apostille can only be issued by the U.S. Department of State in Washington, D.C. — not by a state Secretary of State.

When You Need an Apostilled Form 6166

• Claiming reduced withholding tax on foreign-source dividends, interest, royalties, or pensions under a U.S. tax treaty
• Foreign VAT or sales tax refunds — many EU countries refund VAT to U.S. companies that present a valid 6166
• Treaty benefits in employment income for U.S. citizens working abroad temporarily
• Avoiding double taxation on income earned in a treaty country
• Opening foreign brokerage or business accounts that require proof of tax residency
• Claiming reduced rates on foreign real estate income (rental, capital gains)

How to Request and Apostille IRS Form 6166

1. File IRS Form 8802 (Application for U.S. Residency Certification) and pay the $85 user fee. Submit at least 45 days before you need the 6166 — the IRS publishes processing times of 6–8 weeks.
2. Receive Form 6166 from the IRS — a one-page letter on IRS letterhead with an official signature.
3. Submit Form 6166 to the U.S. Department of State Office of Authentications in Washington, D.C., for the federal apostille. Mail-in turnaround is currently 8–12 weeks.
4. Certified translation — most non-English-speaking countries require a translation of the apostilled certificate into the local language.

Our apostille services handle the State Department submission and international shipping so you don’t have to courier originals to D.C. yourself.

Important Notes

• One per tax year — Form 6166 is issued for a specific calendar year, and many foreign authorities require a fresh one annually. Plan ahead.
• If you need certification for multiple countries, request multiple originals on Form 8802 — each is $85.
• If the destination country is not a Hague member, you’ll need consular legalization instead of an apostille.
• Form 6166 is not required for U.S. tax filing — it exists solely to certify residency to foreign authorities.